L.V. Beethoven "Symphony No. 5 in C minor Op.67" She is a Musicart who carries "Destiny" in her body. Despite her ladylike appearance, her facial expressions rarely change and her tone of voice is always calm and polite. At first glance, she looks pretty, but she has an unconventional personality, with a sharp tongue and a sweet tooth. She and her partner, the conductor Takt, have a deep and long past together.

Spoiler

Cosette used to take care of Takt in his childhood. One day during Symphonica Party, Cosette suggests Takt to play the piano to make his debut as a pianist, which Takt eventually gives into. Cosette joined him in a four hands rendition of popular Uptempo music, impressing everyone. Soon after the performance, the town got attacked by D2, with Takt and Cosette being the targets. Takt managed to survive, however Cosette was fatally injured. Upon her last moments, her white stone pendant (a Harmonia Crystal), awakened Destiny inside her.